Using eddy current probes for non-destructive testing of various alloys is common in a variety of environments. The testing applications include alloy sorting, detecting cracks in airframes and remotely testing structures in hazardous environments, such as nuclear power plant heat exchanger tubing. Such testing applications are frequently essential for quality control and prevention of potentially catastrophic failures of structural members, weldments and other types of joints.
It is desirable to test for structural flaws as deeply as possible for several reasons. One reason is that the access to a potentially flawed location in a test specimen may be limited to a region that is significantly displaced from the potential flaw location. Another is that it is desirable to detect a propagating flaw long before it reaches a critical size or comes close to breaching a barrier such as the barrier between radioactive and non-radioactive water in a nuclear power plant.
An additional consideration in the nuclear power plant application is that eddy current test probes must be relatively small. Typically, an eddy current test probe is inserted in a steam tube past the locations where any flaws are expected and then rotated circumferentially as the eddy current test probe is withdrawn from the steam tube. Therefore, the interior diameters of the steam tubes in a nuclear steam generator limit the physical size of an eddy current test probe and, consequently, the size of the coils in the eddy current test probes. This size limitation, in turn, places restrictions on the physical configuration of a probe and on electrical parameters of the eddy current test coils, and affects the depth penetration of the eddy currents the eddy current test coils generate, as will be discussed below.
Accordingly, it is an objective of the present invention to provide an eddy current test probe with enhanced test depth performance.
It is a further objective of the present invention to provide an eddy current test probe with enhanced test depth performance in space-limited applications such as inside tubulartest specimens.
It is a still further objective of the present invention to provide a test coil assembly with enhanced sensitivity to flaws in test specimens.